The present invention relates to a transaxle device having a pair of high torque, low speed motors. More particularly the present invention relates to a transaxle and hydraulic motors of greatly improved power to weight design to provide on-road and off-road vehicle power.
Once humanity discovered the wheel and put two of them together with an axle, vehicles have been designed for almost every purpose. Broadly, the development of motors has made vehicles efficient devices for moving persons and objects at faster speeds or with more power than otherwise has been possible. Steam and then internal combustion engines changed history, as persons and objects could be transported faster and farther with less effort than ever before.
Whether with internal combustion motors, electric motors, or any such device, power has been derived from rotation of a shaft, such as a crank shaft driven by pistons. The general rule has been the more power that is needed, the faster the revolutions per unit of time of the motor. The only alternative to higher rpms is a larger motor. Hydraulic motors, however, have not been used in many instances as actual drive applications for vehicles, primarily because the requirements of such a motor can""t be met by conventional hydraulic motor designs. The primary drawback is that prior hydraulic motors are designed to drive a shaft, usually in combination with a transmission or gear box. While this would be appropriate for a vehicle using a transmission, such as a lawn mower or other vehicle not requiring much power, hydraulic motors are not as effective over large rpm ranges as the readily available gasoline motors used on such devices.
One form of hydraulic motor that has found use in industry is the low speed/high torque hydraulic motor, although it has not been applied to drive vehicles to this date because of certain drawbacks listed below. These low speed and high torque hydraulic motors come in two basic forms and in a variety of designs. The motors either are gear reduction motors or radial piston motors. In the former, high speed motors are reduced using a complicated series of gears to lower the speed and achieve higher torque. In the latter, various schemes for moving fluids around the axis of a crankshaft have been provided. Neither is suitable for use with, for example, a compact design mounted on a small vehicle where high power is needed. My U.S. Pat. No. 5,897,073 illustrates the use of an improved motor for holding extremely large and heavy spools of those cables. Even in that example, the vehicle itself is diesel engine driven.
Vane motors employ pressure against a plurality of vanes riding on a ring cam to form sealed chambers that carry fluid through the device, optimally at low pressure. The major disadvantage is that there are too many leakage paths. Rolling-vane motors sequence fluid flow to put high pressure against trailing surfaces and low pressure against leading surfaces, but are limited in displacement
There are also a variety of piston motors. Radial piston motors have a wide displacement range and are very efficient in medium or high displacement ranges. Cam type radial piston motors are less efficient and have difficulty at low speed. Axial piston motors are effective and have good starting torque characteristics. Two sources of heavy duty hydraulic motors are Nutron Motor Co., Inc. in Eliot, Me., which produces a radial piston hydraulic motor under the MHA series, and Kawasaki Precision Machinery, Inc. which produces radial piston hydraulic motors at its Staffa facility in Plymouth, England.
One of the principle drawbacks to hydraulic motors is that the commercial designs are extremely large for the power that is produced. Both the space or volume taken up by such motors and the weight that is needed are so great as to be seen as drawbacks or handicaps when selection of a motor is being made. In order to have useful torque in industrial applications, such as in heavy equipment, moveable boat and lumber lifts, end loaders, winches, and other hub drive designs, great amounts of power is needed. However, all presently known designs are not capable of effectively using the power of a short stroke, high displacement motor arranged within a compact area or motor volume so as to be adapted to the device of interest.
It would be of great advantage if an improved hydraulic motor for use with vehicles could be provided that would deliver the same or greater power using less space and having less weight than conventional motors which have been described.
In addition, it would be an advance in the art if high torque, low speed motors could be designed that did not require the use of multiple reducing gears to translate high speed motion into low speed, high torque output.
Also, it would be of significant advance if a vehicle could be provided with a hydraulic motor which could drive each of two wheels on an axle independently, such as when using a transaxle. Such a device could be used to drive each wheel separately, or, in another configuration, drive two tracks independently.
Finally, it would be an advantage if had the capability of self braking, so that no additional brake device would be needed for the vehicle. In other words, it would be a great advance if the motor could stop at any pre-selected point without the use of additional brake elements.
Accordingly, it is an object of the present invention to provide a transaxle device driven by an hydraulic motor capable of operating under high torque and low speed, such motor being suitable for operation in a smaller space than prior art designs.
A further object of this invention is to provide a transaxle device and hydraulic motor configuration capable of producing high torque and low speed without the need for multiple reducing gears to translate high speed motion into the resultant high torque and low speed.
Yet another object of the present invention is to provide a vehicle having a hydraulic motor having fixed displacement of substantially larger capacity than currently available for transaxle applications, so as to provide orders of magnitude more power in a small enough space to operate on both wheels on the axle.
Other objects will appear hereinafter.
It has now been discovered that the above and other objects of the present invention may be accomplished in the following manner. Specifically, the present invention provides a transaxle device of reduced size and increased power, capable of operating under high torque and low speed. The device is suitable for operation in a smaller space than prior art designs, so that vehicles can be equipped with a pair of motors to radically increase the power of any given size of vehicle.
The present invention comprises a pair of hydraulic motors, described below, which operate using hydraulic fluid under pressure from a source carried on the vehicle. The vehicle frame, a structural bridge or other component, is arranged to mount each motor so that the output shaft is operably connected to a wheel. In one embodiment the wheel is a conventional wheel, perhaps with a rim and tire, or, alternatively with cogs for engagement of a track used in bulldozers and the like.
The principal components of the motor or pump include a crank shaft mounted in the housing for connection to a shaft on which a wheel is attached for direct drive. Cylinder and piston assemblies are attached to a crank shaft for rotation upon movement of the pistons in the cylinders to thereby impart motion to the crank shaft and, thus, the wheel shaft or axle.
The hydraulic circuit is designed so that the left and right driving wheels on the vehicle are free to seek their own rate of rotation as the vehicle is steered in turns, while continuing to applying full power to each wheel. The motors themselves can be in one common axle assembly or individually mounted to the vehicle, such as on the main frame or some component attached thereto.